Old Saxon, spoken between approximately the 6th and 11th centuries by an unknown number of speakers likely in the tens of thousands using several dialects, is a member of the Western group of Germanic also including Old Frisian and Old English that was characterized inter alia by a unified pres. pl. marker and no High German sound shift. Saxon territory was bounded roughly by the sea coast in the north, where not occupied by Frisian speakers, and the rivers Rhein and Ysel in the west, Elbe and Saale in the east, and Lippe and Ruhr in the south.

Old Saxon and Old English were close enough that Anglo-Saxon missionaries seem to have been able to communicate easily on Saxon territory. The language is best attested by documents from the 9th C, most prominently by the so-called Hêliand, a story of Christ in 5983 alliterating lines, and the Old Saxon Genesis in 337 lines. The Hêliand, which also shows influence from East Franconian, is of particular interest as a proselytizing document which, while being theologically correct, is couched in terms acceptable to a pre-Christian sensibility of traditional poetics. The Genesis, of which only a fragment exists, was translated into an Old English version of some 700 surviving lines. Beyond these there are smaller attestations, including: the so-called Heberollen, which are lists of tithes to churches or monasteries; blessings; a confession of faith; a renunciation of the devil; single words in manuscripts written in Latin; and personal and place names.